1. Field
One embodiment of the present invention relates to a method of manufacturing a magnetic recording medium such as a patterned medium.
2. Description of the Related Art
In the information-oriented society in recent years, the amount of data to be stored in a recording medium is continually increasing. For this reason, a recording apparatus and a recording medium with an outstandingly high recording capacity have been desired. Also, hard disks, which are currently in an increasing demand as an economical recording medium of high capacity, are expected to be required to have recording density of 1 tera-bit or more per square inch, which is ten times the current density, in coming years.
In a magnetic recording medium used in conventional hard disks, a predetermined region of a thin film including polycrystals of magnetic fine particles is used as one bit for recording. In order to increase recording capacity of a magnetic recording medium, the recording density should be increased. In other words, it is necessary to reduce the recording mark size which is usable for recording of one bit. However, when the recording mark size is simply reduced, the influence of noise which depends on the shapes of magnetic fine particles becomes nonnegligible. If the particle size of magnetic fine particles is reduced to lower the noise, a problem of thermal fluctuation occurs, which makes it impossible to maintain recorded data at a room temperature.
In order to avoid these problems, a bit patterned medium (BPM) has been proposed, in which the recording material is separated by a nonmagnetic material in advance, and a single magnetic dot is used as a single recording cell to perform read and write.
In magnetic recording media installed in HDDs, there is an arising problem of the interference between adjacent tracks which inhibits improvement in track density. Particularly, reducing a fringe effect of a write head field is a significant technical problem to be solved. To solve this problem, there has been developed a discrete track recording-type patterned medium (DTR medium), in which the magnetic recording layer is processed so that the recording tracks are physically separated from each other. In the DTR medium, it is possible to reduce side erase which erases information in the adjacent tracks in writing and side read which reads information in the adjacent tracks in reading. On this account, the DTR medium is promising as a magnetic recording medium capable of providing a high recording density. Incidentally, it should be noted that the term “patterned medium” as used herein in a broad sense includes the bit patterned medium and DTR medium.
In the manufacture of a patterned medium (DTR medium, or BPM), it is an extremely significant problem to reduce irregularity on the surface of the medium, from the viewpoint of flying property of the head. In an ordinary patterned medium, magnetism is separated by using a method such as etching to physically separate the magnetic recording layer. However, if a magnetic recording layer having a thickness of several tens of nanometers is completely etched, the flying property of the head is deteriorated, and as a result, the HDD does not properly function. To overcome this problem, a method of filling recesses is well known. Also effective is a method of deactivating recessed regions as we suggest. In this method, regions of the magnetic recording layer corresponding to the non-recording regions in a patterned medium are deactivated to lose the magnetism thereof, and as a result, a separating effect can be obtained without physically separating the magnetic recording layer.
In patterned media, imprint lithography technique is used to form patterns on the medium. The problem in this case is etching selectivity of the imprinting material to the medium to be patterned. Materials which contain carbon as a main component are preferably used for a mask for the deactivation or the separation of the magnetic recording layer. However, since many imprinting materials show difficulty in having appropriate selectivity to carbon, it is difficult to produce patterns with a good rectangular shape by simply applying the imprinting material on carbon. To solve this problem, Jpn. Pat. Appln. KOKAI Publication Nos. 2005-50468 and 2006-12332 disclose a method in which carbon is used to form a first hard mask, and on the first hard mask, a material having a greater etching resistance than carbon is deposited as a second hard mask, to obtain a two-layered mask. However, most of the materials used as the second hard mask are modified in the process of deactivation, and often remain as residues after removal of the first hard mask, which causes roughness to the surface of the medium.